VEGF is a key player in the formation of new blood vessels (angiogenesis) during embryonic development as well as in a variety of pathological conditions1,2. Although VEGF primarily stimulates endothelial cells, it may also act on other cell types. Indeed, VEGF, VEGF receptor-1 (VEGFR-1/Flt1) and VEGF receptor-2 (VEGFR-2/KDR/Flk1) have recently been implicated in stroke3,4, spinal cord ischemia5, and in ischemic and diabetic neuropathy6, WO 0062798. However, the latter molecules act predominantly via affecting vascular growth or function and a direct effect of VEGF on for example neuronal cells has not been shown11,12. Moreover, the in vivo relevance of such a direct effect is not validated.
Ischemia plays an essential role in the pathogenesis of neurological disorders, acutely during stroke and chronically during aging and several neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Huntington disease. Neurons are particularly vulnerable to oxidative stress by free radicals (generated during ischemia/reperfusion) because of their high oxygen consumption rate, abundant lipid content, and relative paucity of antioxidant enzymes compared to other organs16. Cumulative oxidative damage due to a toxic gain of function of mutant Cu, Zn-superoxide dismutase (SOD1) participates in degeneration of motor neurons in a number of patients with familial amyotrophic lateral sclerosis (ALS)17,18. ALS affects 5 to 10 individuals per 100,000 people worldwide during the second half of their life, is progressive, usually fatal within 5 years after onset of symptoms, and untreatable17-19. Ninety to 95% of cases are sporadic. Although the mechanisms underlying sporadic ALS remain unknown, evidence suggests that oxidative injury, similar to that caused by SOD1 mutations, plays a pathogenetic role18,20,21.
In response to hypoxia, ‘survival’ responses are initiated, including the production of stress hormones, erythropoietin, glycolytic enzymes and angiogenic molecules such as VEGF22,23. Hypoxia-inducible factors (HIFs) play an essential role in mediating this feedback response via binding to a defined hypoxia-response element (HRE) in the promotor of these genes23. Hypoxia is a predominant regulator of VEGF expression as induction of VEGF expression is rapid (minutes), significant (>10-fold) and responsive to minimal changes in oxygen22,23. Surprisingly, little attention has been paid to the possible role of hypoxia and HIFs in the initiation of feedback survival mechanisms in the nervous system. While several neurotrophic molecules have been identified24,25, few have been shown to be regulated by hypoxia. In this regard, it remains unknown whether hypoxic regulation of VEGF provides neuroprotection, independently of its angiogenic activity.
Further in the nervous system, motor neurons are a well-defined, although heterogeneous group of cells responsible for transmitting information from the central nervous system to the locomotor system. Spinal motor neurons are specified by soluble factors produced by structures adjacent to the primordial spinal cord, signalling through homeodomain proteins. Axonal pathfinding is regulated by cell-surface receptors that interact with extracellular ligands and once synaptic connections have formed, the survival of the somatic motor neuron is dependent on the provision of target-derived growth factors, although non-target-derived factors, produced by either astrocytes or Schwann cells, are also potentially implicated. Somatic motor neuron degeneration leads to profound disability, and multiple pathogenetic mechanisms including aberrant growth factor signalling, abnormal neurofilament accumulation, excitotoxicity; autoimmunity have been postulated to be responsible. Even when specific deficits have been identified, for example, mutations of the superoxide dismutase-1 gene in familial amyotrophic lateral sclerosis and polyglutamine expansion of the androgen receptor in spinal and bulbar muscular atrophy, the mechanisms by which somatic mortor neuronal degeneration occurs remain unclear. In order to treat motor system degeneration effectively, we need to understand these mechanisms more thoroughly. Although it has been shown in the art that VEGF has neurotrophic actions on cultured mouse superior cervical ganglia and on dorsal root ganglia (Sondell M. et al. Journal of Neuroscience, (1999) 19, 5731), no studies are available about the possible role of VEGF on motor neurons. The present invention demonstrates that VEGF has a trophic role for neurons, in particular motor neurons, and unveils that defective hypoxic regulation of VEGF predisposes to neuron degeneration. Moreover, the present invention indicates that VEGF is a therapeutic agent for the treatment of motor neuron disorders and relates to the usage of polymorphisms in the VEGF promotor for diagnosing neuron disorders.